1. Field of the Invention
The present invention relates to a surgical prosthesis and, more importantly, pertains to a prosthetic heart valve.
2. Description of the Prior Art
The implantation of prosthetic heart valve began in the late 1950's. These initial efforts were, at best, only marginally successful due to inadequacies in valve design, materials and construction techniques. Undeveloped surgical techniques and a lack of adequate and essential technologies also contributed to the poor results of these first operations. Today, cardiac valve replacement surgery is a highly predictable and successful procedure. It is usually a procedure of choice that provides the patient with significant clinical improvement and overall benefit.
A large number of artificial heart valve designs have been conceived since the initial developement work on heart valves began during the mid 1950's. The majority of these early valves failed either during the laboratory development phase or in the initial clinical evaluation period. Only a few reached the level of clinical acceptance. However, some more recently developed valves exhibit better performance characteristics than earlier developed models. Consequently, the early models, once considered clinically satisfactory and acceptable, are viewed as marginally beneficial and in some cases are obsoleted from existence.
Historically, every widely utilized prosthetic heart valve has had a circular orifice and a conforming flow regulating device such as a ball or disk. This included such caged-ball valves as Starr-Edwards, Smeloff-Cutter, Harken, Braunwald-Cutter, Magovern-Cromie, DeBakey-Surgitool, etc. Caged-disk valves having circular orifices include such prostheses as the Starr-Edwards, Kay-Shiley, Beall-Surgitool and Cooley-Cutter heart valves. The pivoting/tilting disk valve is a modification of the caged-disk valve. It too has a circular orifice. The Lillehei-Kaster, Bjork-Shiley, Wada-Cutter and Hall-Kaster valves are four examples of pivoting/tilting disk valves. The Kalke bileaflet valve developed during the mid to late 1960's is a generic refinement of the pivoting/tilting disk principle. This bileaflet principle was further improved. It is now being evaluated clinically and is known as the St. Jude valve.
In addition to mechanical prosthetic heart valves there is another group of valves known as bioprostheses. All have the general configuration of the natural aortic valve and are constructed from natural tissue or from synthetic materials. Some bioprostheses are aortic valves harvested from other species such as swine. These valves have flexible parts that regulate blood flow similar to the cusps of the natural arterial valves. Like the mechanical devices listed above, the flexible leaflet valves also have circular orifices. All prosthetic heart valves, including mechanical and bioprostheses, are fitted with a sewing ring that completely encircles the valve orifice. The sewing ring is generally confined to the level of the orifice passage. A pliable fabric sewing ring has been found best suited for heart valves to enable the surgeon to firmly attach the prosthetic valve to the natural tissue orifice by sewing or stitching techniques.
Blood flows centrally and with negligible resistance through a healthy natural valve. A diseased natural valve may be restrictive to the free passage of blood and/or incompetent. Therefore, it is desirable to develop prosthetic valves that mimic the desirable conditions of healthy natural valves. The pivoting/tilting disk valves of the Lillehei-Kaster, Bjork-Shiley, Hall-Kaster and St. Jude designs achieve a flow pattern that is more central than any preceding prosthetic valve. However, the flow pattern is diverted from the central axis depending upon the angle of inclination of the disk. The bioprostheses permit the blood to pass centrally through the orifice. But in some cases, the structure of the tissue valve is more restrictive to blood flow than the structure of the pivoting/tilting disk designs.
Until recently, heart valve developers lacked suitable materials capable of withstanding wear over extended periods. Therefore, valves were developed with rotatable (disk) or round (ball) flow regulating devices that would distribute wear and reduce the risk of mechanical failure. With the development of new synthetic materials, an increase in prosthetic valve technology and a better understanding of materials and fabrication considerations, it is now possible to design and develop a satisfactory prosthetic valve with nonrotatable flow regulating occluders. The St. Jude valve is an example of a mechanical prosthesis having an improved central flow pattern and two nonrotatable leaflets.
The heart valve of the present invention provides a mechanical prosthetic valve with true central flow, minimal flow restrictions and negligible wear over extended periods, and produces a better result than existing prostheses of lesser qualities. In addition to improved hemodynamic efficiencies, reduced pressure drop across the valve and increased blood flow, the heart and circulatory system react more favorably to the heart valve having a virtual or functional central flow pattern. It is foreseeable that valvular thrombosis, clotting, a problem that plagues many heart valve patients, is reduced by the heart valve that mimics the blood flow characteristics of the healthy natural valves. The prosthetic heart valve of the present invention with a virtual or functional central flow pattern and exceptional hemodynamic efficiencies produces an improved clinical result when compared with other valves of lesser qualities.